Shallow Foundation Elastic (Immediate) Settlement
Immediate elastic settlement of a footing: a serviceability check, not a strength one.
Example
You enter
- Net contact pressure q (ksf) 3
- Footing width B (ft) 6
- Soil elastic modulus Es (ksf) 250
- Poisson's ratio nu (0.3 sand) 0.3
- Influence factor Is (0.82 rigid square) 0.82
You get
- Se (ft) 0.053726
- Se (in) 0.6447
Checked against published worked examples from: US Army Corps of Engineers.
Details, formula, and sources
ScopeThe immediate (elastic) settlement of a footing - the serviceability check a footing can fail while sitting far below its bearing strength. The theory-of-elasticity immediate settlement Se = q B (1 - nu^2) Is / Es (Is ~0.82 rigid square) gives a 6 ft footing at 3 ksf on medium sand 0.64 in - under the customary 1 in limit - but halve the modulus and the same footing fails at 1.29 in. Sizes the footing against movement, not strength; consolidation and embedment are separate. A design aid, not the geotechnical engineer's report.
Formula or tableSe_ft = q B (1 - nu^2) Is / Es; Se_in = 12 Se_ft.
Source and editionThe theory-of-elasticity immediate (elastic) settlement of a shallow foundation, Se = q B (1 - nu^2) Is / Es, with the shape-and-rigidity influence factor Is (~0.82 rigid square, ~0.95 flexible-square average, larger for strips), as compiled in Bowles (Foundation Analysis and Design) and the customary geotechnical texts, by name.
Free accessThe elasticity-based settlement form and the influence-factor tables are public in the standard foundation-engineering references; the arithmetic is public.
What governsEstimate. AHJ and licensed professional govern.
API field namesq_ksf, b_ft, es_ksf, nu, is_f, se_ft, se_in
- Elastic form Se = q B (1 - nu^2) Is / Es on a deep uniform elastic layertheory of elasticity / Bowles
- Influence factor Is as entered (~0.82 rigid square; ~0.95 flexible-square average; larger for strips)Bowles influence-factor tables
- Scope immediate settlement only; consolidation, layering, and embedment are separatecustomary geotechnical practice